Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$141.98	12.409%	$159.5983	$159.60	$159.60	$159.60
Purchase #2	$164.82	4.257%	$171.8364	$171.84	$171.85	$171.80
Purchase #3	$11.60	9.434%	$12.6943	$12.69	$12.70	$12.70
Purchase #4	$88.95	10.380%	$98.183	$98.18	$98.20	$98.20
Purchase #5	$110.93	6.501%	$118.1416	$118.14	$118.15	$118.10
Purchase #6	$81.47	10.296%	$89.8582	$89.86	$89.85	$89.90
Purchase #7	$12.56	4.344%	$13.1056	$13.11	$13.10	$13.10
7 purchase totals =	$612.31		$663.4174	$663.42	$663.45	$663.40